Superfast compression library
C C++ Lua
Latest commit a05d383 Feb 22, 2016 @gpnuma gpnuma Update


Superfast compression library

DENSITY is a free C99, open-source, BSD licensed compression library.

It is focused on high-speed compression, at the best ratio possible. Streaming is fully supported. DENSITY features a buffer and a stream API to enable quick integration in any project.

Why is it so fast ?

One of the biggest assets of DENSITY is that its work unit is not a byte like other libraries, but a group of 4 bytes.

That is, when other libraries consume one byte of data and then apply an algorithmic processing to it, DENSITY consumes 4 bytes and then applies its algorithmic processing.

As one can easily see, with DENSITY processing happens 4 times less often, therefore it is potentially much faster. But on the other side it also makes DENSITY more difficult to craft, as all well-known compression techniques scale poorly to groups of 4 bytes.

That is why DENSITY's algorithms were designed from scratch. They have to alleviate for 4-byte work units and still provide great speed.

Speed pedigree traits

  • 4-byte work units
  • heavy use of registers as opposed to memory for processing
  • avoidance of or use of minimal branching when possible
  • use of low memory data structures to favor processor cache Lx accesses
  • library wide inlining
  • specific unrollings
  • prefetching and branching hints
  • restricted pointers to maximize compiler optimizations


Quick bench

DENSITY features an integrated in-memory benchmark. After building the project (see build), a benchmark executable will be present in the build directory. If run without arguments, usage help will be displayed.

File used : enwik8 (100 MB)

Platform : MacBook Pro, OSX 10.10.3, 2.3 GHz Intel Core i7, 8Gb 1600 MHz DDR, SSD, compiling with Clang/LLVM 6.1.0

Timing : using the time function, and taking the best user output after multiple runs. In the case of density, the in-memory integrated benchmark's best value (which uses the same usermode CPU timing) is used.

Library Algorithm Compress Decompress Size Ratio Round trip
density 0.12.5 Chameleon 0.098s (1023 MB/s) 0.062s (1619 MB/s) 61 524 478 61,52% 0.160s
lz4 r129 -1 0.468s (214 MB/s) 0.115s (870 MB/s) 57 285 990 57,29% 0.583s
lzo 2.08 -1 0.367s (272 MB/s) 0.309s (324 MB/s) 56 709 096 56,71% 0.676s
density 0.12.5 Cheetah 0.179s (560 MB/s) 0.142 (706 MB/s) 53 156 750 53,16% 0.321s
density 0.12.5 Lion 0.356s (281 MB/s) 0.348s (288 MB/s) 47 818 076 47,82% 0.704s
lz4 r129 -3 1.685s (59 MB/s) 0.118s (847 MB/s) 44 539 940 44,54% 1.803s
lzo 2.08 -7 9.562s (10 MB/s) 0.319s (313 MB/s) 41 720 721 41,72% 9.881s


Squash is an abstraction layer for compression algorithms, and has an extremely exhaustive set of benchmark results, including density's, available here. You can choose between system architecture and compressed file type. There are even ARM boards tested ! A great tool for selecting a compression library.

Screenshot of density results on Squash


FsBench is a command line utility that enables real-time testing of compression algorithms, but also hashes and much more. A fork with the latest density releases is available here for easy access. The original author's repository can be found here. Very informative tool as well.

Here are the results of a couple of test runs on a MacBook Pro, OSX 10.10.3, 2.3 GHz Intel Core i7, 8Gb 1600 MHz DDR, SSD, compiling with Clang/LLVM 6.1.0 :

enwik8 (100,000,000 bytes)

Codec                                   version      args
C.Size      (C.Ratio)        E.Speed   D.Speed      E.Eff. D.Eff.
density::chameleon                      0.12.5 beta  
   61524478 (x 1.625)      973 MB/s 1487 MB/s       374e6  572e6
density::cheetah                        0.12.5 beta  
   53156750 (x 1.881)      524 MB/s  655 MB/s       245e6  307e6
density::lion                           0.12.5 beta  
   47818076 (x 2.091)      292 MB/s  295 MB/s       152e6  153e6
LZ4 fast 17                             r129         
   86208275 (x 1.160)      741 MB/s 2689 MB/s       102e6  370e6
LZ4 fast 3                              r129         
   63557747 (x 1.573)      319 MB/s 1651 MB/s       116e6  601e6
LZ4                                     r129         
   57262281 (x 1.746)      260 MB/s 1676 MB/s       111e6  716e6
LZF                                     3.6          very
   53945381 (x 1.854)      192 MB/s  365 MB/s        88e6  168e6
LZO                                     2.08         1x1
   55792795 (x 1.792)      286 MB/s  370 MB/s       126e6  163e6
QuickLZ                                 1.5.1b6      1
   52334371 (x 1.911)      280 MB/s  353 MB/s       133e6  168e6
Snappy                                  1.1.0        
   56539845 (x 1.769)      238 MB/s  799 MB/s       103e6  347e6
wfLZ                                    r10          
   63521804 (x 1.574)      149 MB/s  512 MB/s        54e6  186e6

silesia (211,960,320 bytes)

Codec                                   version      args
C.Size      (C.Ratio)        E.Speed   D.Speed      E.Eff. D.Eff.
density::chameleon                      0.12.5 beta  
  133118914 (x 1.592)     1129 MB/s 1601 MB/s       420e6  595e6
density::cheetah                        0.12.5 beta  
  101751478 (x 2.083)      578 MB/s  693 MB/s       300e6  360e6
density::lion                           0.12.5 beta  
   87677008 (x 2.418)      323 MB/s  319 MB/s       189e6  187e6
LZ4 fast 17                             r129         
  131735121 (x 1.609)      685 MB/s 2491 MB/s       259e6  942e6
LZ4 fast 3                              r129         
  107062945 (x 1.980)      430 MB/s 2052 MB/s       212e6 1015e6
LZ4                                     r129         
  100883640 (x 2.101)      358 MB/s 2013 MB/s       187e6 1055e6
LZF                                     3.6          very
  102043866 (x 2.077)      254 MB/s  492 MB/s       131e6  255e6
LZO                                     2.08         1x1
  100592662 (x 2.107)      427 MB/s  573 MB/s       224e6  300e6
QuickLZ                                 1.5.1b6      1
   94727961 (x 2.238)      368 MB/s  429 MB/s       203e6  237e6
Snappy                                  1.1.0        
  101385885 (x 2.091)      346 MB/s 1113 MB/s       180e6  580e6
wfLZ                                    r10          
  109610020 (x 1.934)      195 MB/s  698 MB/s        94e6  337e6


DENSITY can be built on a number of platforms. It uses the premake build system.

It was developped ang optimized against Clang/LLVM, therefore it is strongly recommended to compile with Clang/LLVM - especially if you intend to perform benchmarks -, but if that's not possible GCC is also supported, GCC version 5.1 or later being the preferred choice for performance. The following assumes you already have git installed.

Mac OS X

On OS X, Clang/LLVM is the default compiler, which makes things simpler.

1) Download and install premake5 for OS X and make it available in your path.

2) Run the following from the command line :

cd build
premake5 gmake


On Linux, Clang/LLVM is not always available by default.

1) Install Clang/LLVM if you don't have it already (on the Debian distribution for example, sudo apt-get install clang-3.5 should do the trick)

2) Download and install premake5 for Linux and make it available in your path.

3) Run the following from the command line :

cd build
premake5 gmake


On Windows, things are a (little) bit more complicated.

1) First, check if you have git installed, if not you can get it here. Make it available in your path.

2) We'll use GNU make to build the project, on Windows it's not part of the default toolset but you can download a port here. Make it available in your path.

3) Microsoft Visual Studio is required as we will use its linker, get it here.

4) Now we can install Clang/LLVM for Windows, and thanks to the ClangOnWin project it's easy ! You can download it here. Make it available in your path.

5) Download and install premake5 for Windows and make it available in your path (edit the Path environment variable).

6) Run the following from the command line :

   cd build
   premake5.exe gmake

And that's it ! You can now use the integrated in-memory benchmark to test your files (the benchmark or benchmark.exe binary).

Output format

DENSITY outputs compressed data in a simple format, which enables file storage and optional parallelization for both compression and decompression. Inside the main header and footer, a number of blocks can be found, each having its own header and footer. Inside each block, compressed data has a structure determined by the compression algorithm used.

It is possible to add an integrity checksum to the compressed output by using the DENSITY_BLOCK_TYPE_WITH_HASHSUM_INTEGRITY_CHECK block type. The 128-bit checksum is calculated using the excellent SpookyHash algorithm, which is extremely fast and offers a very small performance penalty. An additional integrity check will then be automatically performed during decompression.


DENSITY features a buffer API and a stream API which are very simple to use, yet powerful enough to keep users' creativity unleashed. Please see the quick start at the bottom of this page.

About the algorithms


This is not a so-to-speak algorithm as the name implies. It embeds data inside the density block structures. It can be used to quickly add integrity checks to input data, but it has another important purpose inside each block : if data is marked as incompressible using the target algorithm, a mode reversion occurs and copy mode is instead used for the remainder of the block. On the next block the target algorithm is tried again.


Chameleon is a dictionary lookup based compression algorithm. It is designed for absolute speed and usually reaches a 60% compression ratio on compressible data. Decompression is just as fast. This algorithm is a great choice when main concern is speed.


Cheetah was developed in conjunction with Piotr Tarsa. It is derived from chameleon and uses swapped double dictionary lookups and predictions. It can be extremely good with highly compressible data (ratio reaching 10% or less). On typical compressible data compression ratio is about 50% or less. It is still extremely fast for both compression and decompression and is a great, efficient all-rounder algorithm.


Lion is a multiform compression algorithm derived from cheetah. It goes further in the areas of dynamic adaptation and fine-grained analysis. It uses multiple swapped dictionary lookups and predictions, and forms rank entropy coding. Lion provides the best compression ratio of all three algorithms under any circumstance, and is still very fast.

Quick start (a simple example using the APIs)

Using DENSITY in your application couldn't be any simpler.

First you need to include the 2 following files in your project :

  • density_api.h
  • density_api_data_structures.h

When this is done you can start using the DENSITY APIs :

#include "density_api.h"

#define MY_TEXT "This is a simple example on how to use Density API bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla"


uint8_t *outCompressed   = malloc(BUFFER_SIZE * sizeof(uint8_t));
uint8_t *outDecompressed = malloc(BUFFER_SIZE * sizeof(uint8_t));

 * Buffer API *

density_buffer_processing_result result;
    printf("%llu bytes >> %llu bytes\n", result.bytesRead, result.bytesWritten);

result = density_buffer_decompress(outCompressed, result.bytesWritten, outDecompressed, BUFFER_SIZE, NULL, NULL);
    printf("%llu bytes >> %llu bytes\n", result.bytesRead, result.bytesWritten);

 * Stream API *

// We create the stream using the standard malloc and free functions
density_stream* stream = density_stream_create(NULL, NULL);

// Let's compress our text, using the Chameleon algorithm (extremely fast compression and decompression)
if ((streamState = density_stream_prepare(stream, (uint8_t *) TEXT, strlen(TEXT), outCompressed, BUFFER_SIZE)))
    fprintf(stderr, "Error %i when preparing compression\n", streamState);
if ((streamState = density_stream_compress_init(stream, DENSITY_COMPRESSION_MODE_CHAMELEON_ALGORITHM, DENSITY_BLOCK_TYPE_DEFAULT)))
    fprintf(stderr, "Error %i when initializing compression\n", streamState);
if ((streamState = density_stream_compress_continue(stream)))  if (streamState != DENSITY_STREAM_STATE_STALL_ON_INPUT)
    fprintf(stderr, "Error %i occured during compression\n", streamState);
if ((streamState = density_stream_compress_finish(stream)))
    fprintf(stderr, "Error %i occured while finishing compression\n", streamState);
printf("%llu bytes >> %llu bytes\n", *stream->totalBytesRead, *stream->totalBytesWritten);

// Now let's decompress it, using the density_stream_output_available_for_use() method to know how many bytes were made available
if ((streamState = density_stream_prepare(stream, outCompressed, density_stream_output_available_for_use(stream), outDecompressed, BUFFER_SIZE)))
    fprintf(stderr, "Error %i when preparing decompression\n", streamState);
if ((streamState = density_stream_decompress_init(stream, NULL)))
    fprintf(stderr, "Error %i when initializing decompression\n", streamState);
if ((streamState = density_stream_decompress_continue(stream))) if (streamState != DENSITY_STREAM_STATE_STALL_ON_INPUT)
    fprintf(stderr, "Error %i occured during decompression\n", streamState);
if ((streamState = density_stream_decompress_finish(stream)))
    fprintf(stderr, "Error %i occured while finishing compression\n", streamState);
printf("%llu bytes >> %llu bytes\n", *stream->totalBytesRead, *stream->totalBytesWritten);

// Free memory


And that's it ! We've done two compression/decompression round trips with a few lines !

If you want a more elaborate example you can checkout the SHARC project.

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